Sin(π\3-a)-sin(π/3+a) ?
Sin(π/3 + a) = sin(π/3)cosa + cos(π/3)sina sin(π/3 - a) = sin(π/3)cosa - cos(π/3)sina sin(π/3 - a) - sin(π/3 + a) = sin(π/3)cosa - cos(π/3)sina - sin(π/3)cosa - cos(π/3)sina = = -2cos(π/3)sina = -2 * (1/2) sina = -sina